Spring hinges of the mentioned type are known in the art. The European patent specification EP 0 426 947 B1 addresses a spring hinge for spectacles that has a housing, a hinge element, a spring element and a blocking body. In addition, a spring piston is provided which transmits the forces from the spring element into the blocking body so that the same can be displaced into a locking position. The hinge element, the blocking body, the spring piston and the spring element can be assembled to form a unit which can be inserted as a whole into the housing. Here, it is apparent that in particular the hinge element is manufactured in a comparatively complicated and massive manner which results in high production costs.
The international patent application WO 01/31386 A1 implies a spring hinge which also has a housing, a spring element, a blocking body and a spring piston. Here, the housing serves at the same time as hinge element and is displaced relative to the temple piece during a deflection of the temple piece beyond the stop position in the wearing position in such a manner that the spring element is compressed. The blocking body engages with a snap-in element with the temple piece so that the forces are transmitted into the same and push the same back into the wearing position. To be able to fulfill its function as hinge element, the housing must be guided in the temple piece. For this purpose, viewed in a longitudinal section, a U-shaped guiding groove is provided in which the housing engages with an edge. The disadvantage of this configuration is that not only a complicated hinge element is provided, but also that the temple piece has to be machined in a complex manner to obtain the guiding groove.